I don't know what it is but I think I can tell you how to kill it. It's a broadleaf weed so most weed killers should do the trick. I used ortho weed b gon for southern lawns to help control a broadleaf weed in my Bermuda lawn with great success. I bought the concentrate, mixed it per the instructions, and applied it with a tank sprayer. The weeds were browning within 24 hours and it caused very light if any damage to my lawn.

NO NO NO NO NO NO!!!! Those are very possibly oak tree suckers. If you kill the suckers you will kill the tree. They could also be new oak trees from acorns buried by squirrels. Dig a couple of them up. If they are not attached to larger roots, then go ahead and either dig them out or spray. But if they are attached to larger roots, then just mow them off 2x per week.

How are you watering? Usually these things pop up due to stress on the tree. If you cannot see the root flare at the base of the tree, then unbury the trunk down to the roots. If you are watering briefly every day, then you are killing the tree with drought. Big trees need deep watering on an infrequent basis. Oh, by the way, so does your lawn. If you are watering every day or 2-3 times per week, you are hurting the tree and the grass.

And Sherm? What have you to say? Sounded good 'til the picture showed up.

Still looks like a tree to me. Acorns?? The important thing is that it looks like a plant with a tap root. There are a few tools on the market that allow you to stand up and pluck out tap rooted plants. Weed Hound is the one that seemed to kick off the standing weed tool craze. It takes as long to pluck the weed as it takes to step on the weed. Do you have hundreds of these or just 10s?

It is a broadleaf weed if you don't want it there. That was the theory behind my first post suggesting you don't spray it with a broadleaf killer. If it was root suckers, you could easily kill the tree with a simple broadleaf spray.